Pachypodium bispinosum is a deciduous succulent shrublet, up to 1.2 m tall that produces a massive egg- shaped caudex which gives rise to numerous, much contorted spiny branches bearing small oval leaves and profuse quantities of small, bright pink flowers. Low-growing, similar to Pachipodium succulentum, but with branching shoots and small flowers.
Caudex (tuberous stem): Succulent, partially subterranean, up to 60 cm m tall, 20 cm (or more) thick. In the wild the caudex of P. bispinosum is usually deeply buried, but in cultivation, it is usually grown completely or partially exposed.
Branches: Thin from the tuber, 12-45 (or more) cm long, 4-10 mm thick, erect or spreading, simple or sparingly branched, the youngest pubescent, soon glabrous, the old covered with smooth, papery bark. They are armed with paired straight spines, 10–20 mm long with often a third short intrastipular spine, those of the short shoots clustered and much shorter. Spine cushions puberulous, soon becoming glabrous.
Leaves: Scattered on long shoots and in sessile fascicles (short shoots), the latter from axils of the former, all lanceolate to linear-lanceolate, acute, mucronulate, with margins recurved, up to 2-4 cm long and 2-7 mm broad, leathery, slightly rough above, loosely hairy below, particularly along the midrib. Margin recurved. Stipules spiny, those of the long shoots spreading, 6-18 (rarely to 25) mm long, fine, springing from an almost square leaf-cushion, usually under 2 mm high, those of the short shoots much shorter.
Cymes few- to 1-flowered, at the tips of the branches on the long and short shoots and hence often apparently axillary, sessile; bracts small, lanceolate to subulate, deciduous. Pedicels 2-4 mm long, glabrous.
Flowers: Bell-shaped, light pink in shades of purple to pink with a darker tube 15–20 mm in diameter. Calyx 3 mm long, glabrous or slightly and finely woolly; sepals ovate, acute to acuminate; corolla, infra-staminal part cylindric, slender, 6 mm long, graduallyPachypodium bispinosum passing into the upper funnel-shaped portion, the whole tube 12-18 mm long, purple, hairy within below the stamens. Limb 10-14 mm across: Lobes white to purple (the outer half), broad elliptic, rounded at the tips; anthers almost 4 mm long. Disc deeply 5-lobed, as high as the ovary.
Blooming season: The flowers appear with the leaves from June to December.
Fruit (follicular mericarps): Paired 4-6 5 cm long, tapering at each end, grey pubescent.
Seeds: Numerous, ovoid, compressed, 4-5 mm long with an apical tuft (coma) of whitish hairs 2 cm long.
Remarks: When not in flower, it is almost indistinguishable from Pachypodium succulentum with which it overlaps in distribution. Pachypodium succulentum has thick, bonsai-like branches, and the leaves are less hairy, with margins curling down more distinctly and spines that are shorter.